1. Field of the Invention
The present invention relates to an yttrium-barium-copper oxide powder from which a dense sintered body having an excellent superconducting characteristics is obtainable and a process for manufacturing an yttrium-barium-copper oxide superconducting sintered body by using the above powder.
2. Related Art Statement
In superconducting bodies, to heighten the critical current density that is one of the superconducting characteristics is an indispensable requirement for putting the superconducting bodies to practical use. In superconducting sintered bodies, since high densification of the sintered bodies can increase the critical current density, extensive studies for obtaining dense sintered bodies have been carried out.
Heretofore, as a manufacturing process of YBa.sub.2 Cu.sub.3 O.sub.7 (oxygen nonstoichiometry omitted) super-conducting sintered bodies, there have been known (1) processes wherein a YBa.sub.2 Cu.sub.3 O.sub.7 powder is synthesized and then sintered, (2) processes wherein at least two kinds of powders are mixed together and YBa.sub.2 Cu.sub.3 O.sub.7 is manufactured by reaction sintering, etc.
In the above processes (1) the YBa.sub.2 Cu.sub.3 O.sub.7 powder is generally obtained by mixing predetermined amounts of Y.sub.2 O.sub.3 powder, BaCO.sub.3 powder and CuO powder, followed by calcining at 900.degree..about.950.degree. C. in the ambient atmosphere or oxygen. Other than the above, there is a manufacturing process of YBa.sub.2 Cu.sub.3 O.sub.7 comprising synthesis by a co-precipitation method of a nitrate, oxalate or the like containing a predetermined amount of Y-Ba-Cu, followed by calcination and also a process comprising a gas phase synthesis method to obtain a YBa.sub.2 Cu.sub.3 O.sub.7 powder directly, etc.
The above processes (2) include a process wherein a mixture of a Y.sub.2BaCuO.sub.5 powder with one kind or more of unknown phase powders (hereinafter referred to as "A-powder") is obtained by mixing predetermined amounts of Y.sub.2 O.sub.3 powder, BaCO.sub.3 powder and CuO powder, followed by calcining at 900.degree..about.950.degree. C. in vacuum (under an oxygen partial pressure of 10.sup.-4 atm. or less).
In the above-described processes (1) there has been presented a problem that dense sintered bodies cannot be obtained due to a poor sintering ability of YBa.sub.2 Cu.sub.3 O.sub.7. Although the densification is possible to a certain extent by providing a YBa.sub.2 Cu.sub.3 O.sub.7 fine powder by a co-precipitation method, a gas phase synthesis method or the like, there have been disadvantages such as a difficulty in composition control and an extreme cost increase.
In the case of the above-described processes (2), where the mixture of a Y.sub.2 BaCuO.sub.5 powder with A-powder is used, dense sintered bodies can be obtained owing to an excellent sintering property. However, A-powder has such a high reactivity with moisture, carbon dioxide and oxygen in the ambient atmosphere that difficulties have been encountered in storage and handling of A-powder.